Vulcanization process



United States Patent O 2,941,979 VULCANIZATION PROCESS Hans Pohle, Leverkusen, and Friedrich Lober, Leverkusen-Bayerwerk, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed Feb. 6, 1957, Ser. No. 638,458 Claims priority, application Germany Feb. 8, 1956 3 Claims. (Cl. 260-453) The present invention relates to an improved vulcanization process, more particularly, it concerns the process of improving the mechanical properties of rubber vulcam'zates.

p-Phenylene diamines which may contain alkyl-, isoalt kyl-, cycloalkylor aryl radicals in varying combinations attached to the nitrogen atoms, have heretofore been used as antioxidants in vulcanizates made of natural or synthetic rubber. These compounds are added to the vulcanizates to render them stable to fatigue and to attack by ozone. Among the best known products of p-phenylene diamines are N,N'-diphenyl-p-phenylene-diamine, and N-cyclohexyl-N-phenyl-p-phenylene-diamine.

Furthermore it is known that the resistance to ageing and fatigue effected by 2,2,4-trimethyl-dihydroquinolines which are unsubstituted in the aryl radical is inferior to the protective effect achieved with p-phenylene diamines. Moreover, 6-ethoxy-2,2,4--trimethyl-dihydroquinoline has been proposed as protective agent against attack by ozone.

However, as compared with compounds useful for obtaining protect-ion against attack by ozone, for instance compounds of the p-phenylene-diamine series, the aforesaid compound provides only an unsatisfactory protection against formation of cracks under dynamic stresses and a minor protection against attack by ozone.

In accordance with the invention it has now been found that an improved protective effect against the formation of cracks of the vulcanizates under dynamic stresses can be imparted to vulcanizates of natural and synthetic rubber by adding to the rubber mixtures prior to vulcaniza tion a mixture of the afore-defined p-phenylene diamines and 2,2,4-trimethyl-dihydroquinolines of theformula.

,In general, it is advantageous to add to the vulcanizates.

Patented June 21, 1960 the mixture of p-phenylene-diamines and 2,2,4'trimethyldihydroquinolines at a proportion of -25 parts of the p-pheny-lene-diamine and 25-75 parts of the 2,2,4-trimethyl-dihydroquinoline. The most favorable mixing proportion to be chosen in a specific case can easily be determined by a preliminary test.

The mixture of p-phenylene diamines and 2,2,4-trimethyl-dihydroquinol-ines is added to the rubber mixtures in amounts customarily applied in the art. In general, the mixture is added in a proportion of 0.1- 5%, preferably 0.253%, referred to the amount of rubber. In specific cases it may be advantageous to add larger quantities of the mixture. Moreover, it is possible according to the invention to add the mixture proposed according to the invent-ion in combination with previously known antioxidants.

The hereindescribed antioxidants may be used for natural rubber and synthetic rubber-like polymers obtained for instance from conjugated diolefins or copolymers of conjugated diolefins with polymerizable vinyl compounds such as styrene, acrylonitrile, a-crylates and methacryl-ates and similar compounds.

The invention is further illustrated by the following examples without being restricted thereto the parts given by weight, if not otherwise stated.

EXAMPLE 1 t is divided into 6 parts and each part is mixed with one of the following antioxidants or mixture of antioxidants. The antioxidants are added at a proportion of 1% by weight each referred to the rubber content. N., I-.dip -p-p eny -d n (2) A mixture consisting of 75 parts N,N"- diphenyl-p phenylene-diamine and 25 parts of 6-.ethoxy-.2,2,4-tri- J methyl-dihydroquinoline;

(3) A mixture consisting of 65 parts of N,N'-diphenylp-phenylene-diamine and 35 parts of 6-ethoxy-2,2,4-trimethyl-dihydroquinoline;

(4) A mixture consisting of 50 parts of N,N '-dipheny1- p-phenylene diamine and 50 parts of 6-ethoxy-2,2,4-trimethyl-dihydroquinoline;

(5) A mixtureconsisting of 25 parts of N,N'-diphenylp-phenylene diamine. and 75 parts of 6-ethoxy-2,2,4-trimethyl-dihydroquinoline;

(6) 6-ethoxy-2,2,4-trimethy1-dihydroquinoline.

The mixtures obtained are vulcanized in the form of profiled tests specimens of a thickness of 12 mm. at 2.1'

atmospheric gauge=134 C. for minutes each. The test specimens are then connected with one another to form an endless belt and subjected on a test machine of thetDu Pont type (cf. Vanderbilt Rubber Handbook II. ed. (1936), page 164) to dynamic stresses of alternatmg bending (3.5 million times). The figures in the following table represent the estimated formation of cracks,

which distinctly depends on the quantities of the components added to the vulcanizates.

TestNo 1 2 a 4 5 6 v 3. r The figures indicate the degree of crack formation as follows:

means no cracks. l'means crack formation starts;

2 means pronounced crack' fo'rmat iont 3 means ruptures over 4mm. length? EXAMPLE 2 1 Therubber mixture describedin Example l is divid edinto7 parts and each ,part-is mixed "with one of .the antioxidants oram'ixturetof'antioxidants indicated below, The antioxidants are added atta proportion of 115% .by weightreferredtb the rubber content..

(1) N-cyclohexyl-N'-phenyl-p5pheriylnea diamine;

(2)"A mixture consisting'off75 parts of .cylclohexyl N phcnyl pfphenylene diamine and 25 parts of 6='ethoxy- 2 2;4 trimethyl dihydroquinoline;

(3) Amixture consisting of 65 parts ofN-cyclohexyl-L N'-pheny l-p-phenylene diarnine and SSparts of 6-etho'x'y-Zj2;4=trimethyldihydroquinoline;

(4) A mixture c'ons'istingof SO'partsof N-cyclohexyl- N pheny1-p-.phenylene ,diamine and 'SO'parts of 6-ethoxy -2,2 ,4trimethyl-'dihydroquinoline;

(5 A'mixture consisting of 35 "parts of N-c'ycloh'exyh N' -phenyl-p-phenylene diamine'a'nd 65parts of6-ethoxy 2y2A-trimethyl-dihydroquinoline;

(6) Arn'ixture consisting of 25 parts otN-cyclehexyle N-pheny1-p-phenylene diamine and 75' parts of 6=ethoxy-'" 2,2,4-trimethyl-dihydroquinolinea f (7) 6-ethoxy-2,2,4trimethyl-dihydroquinoline.

The mixtures obtained are-vulcanized'inthefdrnr of profiled test specimens of a thickness ofi12 mm; at*135 for '65 minutes. The-test .specimens arethem-connected. with one another -tot-forrn 1 an .endl'ess belt a asdescribed in Example 1, which is placed on atest machine-- ofgthe Du Pont type (see Example 1) and subjectcd to stressesof alternating bending (3.8 millionntimes); Depending on the quantitative proportion of the components zadded' crackformat-ionis as fo'llowsz.

' Thckfiguresehave the meaning indicated in-Example lz ExAMPL-B a A rubber mixture ofthecornpositiongdescribcd mple; 11 idividediinto 5 parts: andueach, iisxmizc withtonct of the antioxidants or mixtures ,of antioxidants: given below. The antioxidants areeadded .atttaltpropple tion of 1 %tref erred,to,the rubber content-v,

(1)"A' mixture consisting 01365v pa 'tsiof ,N,N'-dipheny11 p-phenylene diainine and 35 PaItS 0f;.6eSeCaHb11t/OXY12ZAfi trirnethyl-dihydroquinoline; I

,A mix uretconsisting of 5-0ipi rts of N,N'\-diphenlylp ephenylene diamine an d 5.0 parts of,6 sccebutoxy 2,2,4-t trimethyl dihydroquinoline;-t

(3 A mixture c0nsisti1igof35 parts ofNJflT-diphenyh. p phenyle'ne diamine and. 3651 parts of .6:sect-butoxy;2,2,4 trimethyhdihydroquinoline;. I

(4)'fA mixture consisting of.25-' parts of, N,I I'--diphenylpeph'enylene diamilie and 75 parts of 6'-' 'sec.,-butoxy-,2,2,4e trimethyl-dihydroquinoline.. v

The mixtures obtained are vulcanized in :the. forrnrzof. profiled test specimens of 'a..thick'ness (of 12. mm; at 2.1, atmospheric gauge=134 Cf fQILBO miIllltflS each, a The; test :specimens :are then connected with one anothervto-n form an ndless -belt asflsctibciilLExample-1,..placedon a ,testmachine of the Du Pontttype vandtsubjectedttoe d namic, stresses by. r ernat ng bending (2L5w millient times). Depending on the quantitative proportion of the components added to the vulcanisates, the formation of cracks is as follows:

TestNo 1 The figures have the meaningindicatedfinrExampiet 1.

EXAMPLE 4= A rubber mixture =consisting of-i parts -of":a:copolymerizate of butadiene and styrene, (typ e. GRS 1500), 50 parts of a high abrasion furnace black, 5 parts of zinc oxide, 3 parts of a petrol origin softener (type Circosol O'il-ZXH); 3 parts -of"'a petrol origin softener (type Parafluib-2016), 1 part 'of 'stearic acid; 1.2" parts: of sulfur; 1- part of benzothiazol=2 cyclohexylsulfenamideand 0.2 part of a condensation product of butyl aldehyde a'ndianiline is'devided into-4' parts; Each part-is mixed. with" 1% by" weightgreferredto' the" rubber content ofth'e mix'ture withone of-the following-mixtures:

(1) A mixture consisting'of 65 parts of N',N" -diphenyI-' p phenylene diarnine' and"35 parts of -6 -sec.-butoxya2;2,4- trimethyl=dihydroquinoline;-

(2) Amixture consisting of '50 parts-of -N,N'diph;c nylpphenylene' diamineand;=50 parts-of 6sec-.ebutoxy 2,2,4.' trimethyl-dihydroquinolineg' (3) A -mixture consisting of 35 parts of N,N'- diphenylp phenylene -diamine-and-65 parts of 6 sec:-butoxy-2,2', 4-' trimethyhdihydroq iinoline;

(4)"'A-mixture consisting of 25 parts of N,N' diphenyl= p-phenylene diamine and 75 parts of 6-sec.abutoxy-2;2,4-' trimethyl dihydroquinoline. I V I The-miXtures-Obtained are vulcanized in the form of profiled testspeciinensj-of a thickness' of 12' mm. and a-'width=-of"22"mm=- for65 minutes at '3 atmospheres gaug'e='l43" G. Thetest specimens are then; connected with-one=another -as described-in-Exampie 1 to rmmm endless belt and su'bjected'in the open-air ongatest ma= chine i ofthe Du Ponttype to dynamicstresses of alternatingbending (8 million times). figures-== represent the estimated-- formation ofcrackswhic'h distinctly depends on" the quantities' of the components-added to the vulcanisatesr Test N o 1 2 3 4 Formation of cracks (estimated); 1-2

The figures have me same meaning as indicated in Example 1.

We'claim:

1: An improved rubber vulcanizate' selected from thegroup consisting: of "natural rubber and a synthetic" rub benys. copolymer t of butadiene-and styrene, said vulcani dihydroquinoline substituted in the phenyl radicahbyam alkoxygroup;

- 27-)- A-ngimproved" rubber .vulcanizateselected from thet group, consisting 10f inatu'nal': rubber and: assynthetic rubabBIYg cop'plymerr of *butadiene and; sty'rene,:.said. Vulcan-,1:

izate being inhibitedjagainst;flcxrcrackingjby the-incom ponaticmztherciilrtprior to vu1eanizatien,-1.o 0;i+S.%z by The following weight of a mixture consisting essentially of (1) N-cyc1o hexyl-N'-phenyl-p-phenylenediamine, and (2) 6-ethoxy- 2,2,4-trimethyl-dihydroquinoline.

References Cited in the file of this patent FOREIGN PATENTS Great Britain May 4, 1939 

1. AN IMPROVED RUBBER VULCANIZATE SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND A SYNTHETIC RUBBERY COPOLYMER OF BUTADIENE AND STRYENE, SAID VULCANIZATE BEING INHIBITED AGAINST FLEX-CRACKING BY THE INCORPORATION THEREIN, PRIOR TO VULCANIZATION, OF 0.5-5% BY WEIGHT OF A MIXTURE CONSISTING ESSENTIALLY OF (1) 75-25 PARTS OF A P-PHENYLENE DIAMINE DERIVATIVE SUBSTITUTED AT THE NITROGEN BY A MEMBER SELECTED FROM THE GROUP CONSISTING OF AN ALKYL-, ISOALKYL-, CYCLOALKYL-, AND AN ARYL GROUP, AND (2) 25-75 PARTS OF A 2,2,4-TRIMETHYLDIHYDROQUINOLINE SUBSTITUTED IN THE PHENYL RADICAL BY AN ALKOXY GROUP. 